Barbier reaction

What is Barbier reaction?

The Barbier reaction is a one-step reaction that allows the synthesis of alcohols from organic halides and carbonyl compounds such as aldehydes or ketones.

Barbier reaction - Barbier-type reaction - general reaction scheme
Barbier reaction

The Barbier reaction was discovered by Barbier in 1898, which was only two years prior to the well-known Grignard reaction. While the Grignard reaction involves the reaction of alkyl halides with magnesium to form Grignard reagents, which then attack carbonyl groups to create carbon-carbon bonds, the Barbier reaction involves mixing both alkyl halides and carbonyl compounds with magnesium turnings, resulting in the formation of carbon-carbon bonds in a single step.

This process allows for the use of a smaller excess of toxic halides and simplifies the purification procedure. It is often preferred for halides such as allyl and benzyl bromides, and is believed to proceed through the single-electron transfer (SET) process.

Various zero-valent metals have been successfully applied to similar reaction conditions, including lithium, which often results in exceptional yields. Metal halides have also been applied to this reaction.

One significant advantage of the Barbier reaction over the Grignard reaction is its tolerance for water, and many metals have been reported to be effective in mediating the aqueous Barbier reaction, including aluminium, antimony, bismuth, cadmium, gallium, indium, lead, magnesium, manganese, samarium, tin, and zinc.

Nonpolar solvents favor R-regioselection, whereas polar solvents like DMSO, which strongly coordinate with the tin of an allylic tin, lead to γ-syn selection. The versatility and mildness of this reaction have been extensively reviewed.